Repeater circuits



April 17, 1928. 1,666,676

B. G. BJRNsoN REPBATER CIRCUITS Original Filed June 27, 1925 o of* luf. ,a f7 il Einw I ZZ ,C

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Patented Apu.' 17, 1928.

UNITED STATESI 1 1,666,676 PATENT OFFICE.

BJRN G. BJRNSON, OF NEW YORK, N. Y., ASBIGNOB T WESTERN ELECTRIC l..

' *,PANY, INCORPORATED, OF NEW YORK, N. Y., A. CORPORATION 0I' NEW YORK.

BEPEATEB CIRCUITS.

Application tiled June 27, 1925, Serial No. 39,884. Renewed April 85, 1987. i

This invention relates to transmissionsystems and particularly to such systems which include repeaters or relaying arrangements for the reenforcement of the transmitted' energy.

More specifically, the invention is applicable to electrical circuits of the type oontaining' apparatus, the operation of which is based on the transmission of short elecl" tric-al impulses, such as voice-operated repeaters and the like.

An object of the invention is to provide a method of and means for reducing the effect of line noiseI on the operation ofrel5 peater circuits or similar apparatus.

One of the greatest sources of trouble encountered in connection with the operation of circuits such as voice-operated repeaters and 'the like is so-called line noise. Voicecontrolled repeater circuits have been devised which operate very satisfactorily on quiet lines, but are either commercially inadequate or afford poor quality on noisy lines. It has heretofore been proposed, in

connection with systems .using voice-oper ated relay systems to utilize a fixed negative potential on the grid of a relay-controlling vacuum tube to prevent false operation of the relays due to line noise. A difficulty with such systems, however, is that, as the source of fixed negative potential must be adjusted for the maximum permissible noise on the system, poor articulation will be obtained as the noise decreases from its maximum value.

In accordance with the present invention, false operation of impulse or voice-operated relays is prevented by providing means for producing on the grid of a relay-controlling 4o vacuum tube a negative potential varying in proportion to the amount of noise on the system, thus giving efiicient articulation un der all conditions. This varying negative potential is obtained by diverting a portion of the noise energy through an auxiliary circuit comprising ay rectifier feeding into a -delay circuit, the output terminals ot which are connected across a. resistance in the input circuit of the relay-controlling tube.

The operation of the circuit ofthe invention is based on the following principles: lVliile voice transmission is intermittent, speech energy being transmitted in pulses of short duration corresponding to words spoken, the noise energy on a line, while varying from time to time, for such short 'intervals of time may be considered as substa-ntiallyA constant. The noise l'energy received over the line can be made to produce a negative grid potential on the relay-con'- trolling tube in a voice-operated re atei' of such magnitude that the relays will not be kept operated by the noise. Obviously, the speech receivedover the line will also produce a negative potential on the grid of the relaycontrolling tube, but by delayin the building up of this negative potentia the switching relays may be operated before it becomes effective. This negative 'grid potential should be proportional to the noise energy and its maximum value should correspond to the maximum permissible noise, as otherwise it will also finally prevent speech from keeping the relays operated during the whole time of a speec impulse.

The invention may be more fully unders tood from the following detailed description when read lin connection with the acccmpanying drawing, in which Fig.l 1 shows a diagrammatic illustration of a portion of a voice-operated'repeater circuit embodying the invention, and Figs. 2 and 3 show curves illustrating the operation of the system of Fig. 1 and the theory on which the invention is based.

In Fig. 1 the noise protective device of the invention is illustrated as applied to an amplifier-rectifier circuit used for operating switching relays in a voice-operated repeater system.) The section L, of the line leading from the voice-operated repeater (not shown) is associated through an input transformer 1 with the input circuit of the main amplifier-rectifier tube 2, which is of the-well known three-electrode type having a cathode or afilament 3, an anode or plate 4 and a grid or control electrode 5. The line Ll is also associate/d through an input transformer 6 with the input circuit of an auxiliary amplifier-rectifier tube 7, also of the 100 three-electrode type, the output circuit of which is connected to the input of a delay circuit 8. The delay circuit 8 may be a lowpass filter of the type` for example, illustrated in Fig. 7 of U. S. patent to Campbell 105 1,227,114. May 22. 1922. The output termi- `nals of the delay circuit 8 are connected across to a resistance 9 in the input circuit of the rectifier tube 2, any portion of which resistance can be placed in series in the .inllo put circuit. Resistances 10 and 11- are con-l nected across the input circuits of rectifiers 2 and 7, respectively The input circuit of rectifier 2 includes in seriesthe cathode 3, the grid battery12, the resistance 9, the resistance 10, and! the grid 5.

The output circuit of rectifier 2 includes inseries the anode 4, the winding of switching relay 13, the plate battery 14, and the cathode 3. A condenser having a capacity of the order of 0.1 microfarad is .preferably connected in shunt to relay 13. A suitable battery is provided for heating the hathode 3 to incandescence. The usual filament, grid and late batteries are also provided in the circuit of the rectifier tube 7.

The leads from the delay circuit 8 are so `connected across the resistance 9 with res ect to the leads across the resistancev 10 t iat energy from the line L1 passing through the auxiliar circuit comprising the rectifier 7 and the de ay circuit 8 will produce a negative potential on the grid of rectifier 2. The low-pass filter comprising the delay circuit 8 in the auxiliary circuit serves two purposes:

y (1) it roduces a smooth rectified current;

and" (2S) line L2 are connected together through lead 17, the back contact of relay 13, the normally closed contact of a hangover relay 18, and lead 19. When the operating winding of relay 13 is energized, relay 13 closes its front contact` causing the operating winding of relay 18 to be energized so as to operate that relay, the energizing circuit extending from grounded battery 20, through the operating winding of relay 18, front contact of relay 13, and lead 17 to' ground. The right-hand winding of hangover relay 18 is closed through a suitable variable resistance 21.

For an ideal condition from the standpoint of articulation, it is desirable that the magnitude of the negative potential on the grid 5 of the relay-controlling rectifier tube 2 at all times should be such that it is just sufficient to prevent operation of the relay 13 by the noise on the line. That is, the negative potential on the grid of the rectifier: 2, and, therefore, the voltage across the resistance 9,

' required to prevent operation of the relay 13 Yby the voltage produced by the noise on the should be adjusted so that the maximum value of this grid potential corresponds with the maximum permissible noise, -as otherwlsef'this negative potential would finally prevent speech from keeping the relay 13 `operated during the whole time' of apspeech impulse.

'lhe ideal relation between the noise voltage and the ne ative grid potential is shown by the curve a) in Fig. 2. The relation vbetween the noise voltage and the negative grid potential which maybe obtained by the circuit of Fig. 1, without the use of the rid battery 12 is illustrated in the curve (b of 'Fig 2. Curve of Fig. 2 illustrates how the addition of, the small grid battery12 to nated -EG, the maximum value of negative' grid potential corresponding to the maximum ermis'sible noise is vdesignated as EM,

otential o n and t e potential of grid battery 12 is designated `as -EB.

The operation of the noise protection circuit of Fig. 1 will now be explained in connection with the curves of Fig. 2 and Fig. 3. It will be assumed, for explanation purposes, that there is some noise on the line when speech is not being received. IThis noiseenergy for any small interval of time may be considered as constant. The noise energy received over the line L1 divides, the part` transmitted through the input transformer 1 being impressed on the input circuit of rectifier 2 across resistance 10, and the partt-ransmitted through the in ut transformer 6 being rectified in the recti er 7, transmit-ted through the low-pass filter 8, and impressed on the input circuit of rectifier 2 across ythe 4 variable resistance 9. As the drop in potential in the variable resistance 9 opposes the drop in potential in the resistance 10, the resistances 9 and 11 may be so adjusted that the maximum voltage across resistance 10 will be less than the rectified voltage across resistance 9. The negative potential on the grid, then, will be that produced by the rid battery 12, or -EBas shown in curve (0% of Fig. 2, which is made of just sufficient magnitude to prevent operation of the relays 13 of rectifier 2.

Now, if the noise energy on the line received over the line L1 varies, the drop of potential inthe variable resistance 9 will vary accordingly and in combination with the battery 12 roduce a negative potential on the grid 5 o the rectifier 2 in accordance withfhe dotted curve in Fig. 2 (c), .this potential being of just sufficient magnitude to prevent the production bythe noise of a cur-4 rent in the output circuit of tube 2 of sufficient magnitude to operate the relay 13.

Now, if an iuipulse of speech energy is received from the repeater circuit over the line L1, the rtion transmitted, together with part of t e noise on the line-` through transformer 1 and impressed on the input circuit of rectifier 2 across the resistance 10, causes the production of a voltage of such amplitude as fo overcome the negative potential on the grid 5. A rectified current will be thereby produced in the output circuit of tube 2 of sufiicient amplitude to o erate relay 13, which in turn will cause t e operation of the hang-,over relay 18. The portion of the speech energy transmitted, together with part of the noise on y.the line, through the transformer 6, is rectified by the rectifier 7, transmitted through the delay circuit 8, and impressed on the input circuit of tube 2 across variable resistance 9. This energy will, of course, produce a negative potential on the grid 5 of rectifier 2 of sufficient magnitude to prevent operation of the relay 13,

but the delay circuit 8 will delay the buildingv up of this nega-tive voltage so 'that the switching relay 13 will be operated by the speech energy in the main circuit before it becomes effective. The'whole output voltage of input transformer, therefore, is available until the auxiliary circuitstarts up to build a negative grid potential across the variable resistance 9.

The time of operation of the relay 13 varies from syllable to syllable, and if there is n.0 noise protecting negative `grid potential,

it might be anywherefrom .002 to .02 of a second. As the delay in the circuit may be made greater'than .02 of a second, the speed of operat-ion of the circuit will be about the same as if the circuit were adjusted for a quiet lille. The building up of the voltage across the resistance 9 should be delayed by the delay circuit 8 for such a length of time that the voltage produced by the voice currents across resistance -10 at that time shall have risen to a highervoltage than the maximum across resistance 9. When the maximum negative grid potential produced b the speech and noise transmitted througi the auxiliary circuit becomes effective, the input volt-a e to the rectifier 2 will be decreased. T is ldecrease in voltage. however, Will not be sufficient to cause relay 13 to release, as at that time the voltage produced by speech across resistance 10 will be greater than the saturation voltage across re,

sistance 9 and also only a small currentis needed to keep relay 13 operated although a relatively large one is needed to operate it -word or syllableis illustrated in Fig. 3,

curve (a)v of that figure showing the varia.-

tion with time of the electrical energy representing a word or impulse, curve (b) the corresponding va'riation with time produced thereby in the rectified current in relay 13,' and curve (c) the corresponding variation with time in the ne ative potential. produced by the s eech impu se on the grid of' the rectifier tu e 2. ln these curves, th ordinates represent. electrical energy, voltage or current, and the abscissas time.

Referring to the curves, it will be noted that when the speech impulse is received, the current in the relay Windin 13 starts to increase at once'and will be o sufficient amplitude to operate this relay at some time A before the auxiliary circuit, comprising the rectifier 7 and the delay circuit 8, begins to build up negativej potential on the grid of rectifier 2. The operation of the relay 13 causes the oper tion of the hangover relay 18 at a slightly atei' time, indicated by B in the curves. At some time C near the end of' the speech impulse, the rectified current in the relay winding 13 will decrease sufficiently,

due to the building up of the negative potential on the grid 5 of rectifier 2, so that relay 13 releases. The release of relay 13 will also cause the release of hang-over relay 18. Variable resistance 21 is adjusted so that the tim-c of relaxation of this relay is such that its release occurs at but a slightly later time D after the end of the speech impulse, thus pfii'eventing part of the Word from being cut o v It is desirable to design the delay circuit 8 so thatit will first give an absolute delay and then a quick rise of the negative voltage on the grid 5 of rectifier 2. If the time of rise of this voltage is too long, the circuit may be sluggish in adjusting itself fo variations in the noise received over the line L1. Also, at the end of a word, the time interval that has to be'considered is the absolute time delay plus the time of decay of the negative potential on the grid 5 of rectifier 2. This time interval should be shorter than the time of relaxation of the relays 13 and 18, as otherwise a syllable might find the negative potential produced by the preceding syllable still effective on the grid of rectifier 2. This condition may be prevented by making the time of relaxation of the hang-over relay 18 long enough lo take caie HNI llO

listeners side. of the repeater, and onl' then if it happens between syllables when t c circuit is in neutral position. The interval of time in which the circuit-would bc biased by the noise against the talker would in prac-A tically every case be smaller than the time delay in the auxiliary circuit. This time delay can' be made usinall enough so that it interferes very slightly and will vnot even be noticed in'ai'i ordinary conversation.

The advantage of. the noise protection circuit ot' Fig. 1 over any circuit utilizing a fixed negative grid potential forA vnoise iroectioii is quite marked. As stated be ore, if a fixed negative grid battery is used it will have 't9 be adjusted-for the' maximum permissible noise on a line'. Under these conditions the articulation ywill get Worse as the noise decreases from its maximum value-due to the longer switching time required, or, in other words, the articulation will be'best when the maximum permissiblenoise is on the line and W'orse when there is no noise on the line, The noise protection circuit of the invention, however,

produces a negative potentialat all times,

' which is just sufficient to neutralize the eect of the line noise.

The circuit of the 4invention is particularly suitable for protecting voice-operated repeaters of both the neutral and biased types against noise, but it is-n'ot limited to voice-operated repeaters, but maybe applied for noiseprotection in any circuits containing apparatus, the operation of whichv i-s based on the transmission `of? 4short impulses of energy. The system illustrated in the drawing and described above should be construed merely asl typical and not as limiting the invention, the scope of which is defined inthe appended claims.

What is claimed is: 1. The method of discriminating between momentary im ulses of current and relatively steady over a circuit in their effect on va receiver circuit, comprising utilizing part of thereceived energy to operate the receiver circuit, separately utilizing part of the received energy to bias said receiver circuit against operation, continuously neutralizing the operating energy due to said steady disturbing currents with the biasing energy dueto said disturbingcurrents, and delaying the efl'ect on said receiver circuit of the biasing energy due to said momentary impulses with respect to the effect on said receivercircuit of the operating energy due to said momentary impulses, thereby linsuring operation of said receiver circuit by said momentary. impulses.

. 2. In a transmission system, av path over which momentary impulses of current are transmitted and subject to relatively steady disturbing currents, a receiver circuit, means isturbing currents received to utilize part bf. the energy received over said path to operate said receiver circuit, means to separately utilizepart of the re. ceived energy tobias said receiver' circuit against operation, means tov continuously neutralizethe effect on said receiver circuit of the operating energy due to said disturbing currents with the biasing 'energy due to said disturbing currents and means to i delay the effect 'on said receiver c ircuitof the biasing energy due to said momentary-y impulses with respect to the effect on said .receiver circuit of the operating energy by an interval sufiicient lto enable operation of said receiver circuit by'said momentary impulses. .3. In a signaling system, a space discharge repeater, input and output circuits therefor, a current responsive device in said output circuit, a line connected to said input circuitover which waves'of rapidly vvarying amplitudeare transmitted and subject to disturbing waves of slowly varying amplitude, means for neutralizing the effect of said slowly varying Waves on .said in- -put circuit, and means for causing said rapidly varying waves to control the operation of said current responsive device.

4. In combination, a line over which momentary impulses of current are transmitted, and subject to relativelyy steady disturbing current, a receiver -element responsive lto said energy impulses, an electron discharge device :fed by said line and feeding said receiver element, said electron discharge device including a control electrode, means to Aproduce on'saidcontrol electrode a negative potential varying in accordance with said disturbing currents and of sufiicient magnitude to prevent disturbing variations from vmitted through said device, means to produce on said control electrode a negative potential varying in accordance with said disturbing-variations, such as to prevent the transmission through said device ofds'turbing variations of sufficient amplitude to effect the operation of said receiver element, and means to delay the building up of a negative potential Yon said control element by one of said momentary impulses until after said device has been operated to repeat said one impulse.

6. In a signaling system, a line over which energy comprising momentary impulses of current and relatively steady disturbing variations is transmitted, an electron discharge device fed by said line, said electron discharge device having a control electrode,

through said device, and means to delay' the production on said control electrode of a negative potential by one of said momentary impulses until after said one lmpulse has been propagated through said device.`

7. In combination, a line over which momentar impulses of current are transmitted and su ject to relatively sustained disturbing currents, an electron discharge device comprising an input and an output circuit, a -receiver element in said output circuit responsive to Waves transmitted through said device, means to'impress part of the energy received over said line on said input circuit in a sense to render said device operative to transmit, separate means to impress part of the energy received over said line on said input circuit vin a sense so as to bias said device a ainst operation, said separate means being a justed with respect to the first mentioned means so that the resultant effect of said sustained disturbing currents is at all times such as to prevent the operation of said discharge device by said sustained currents, and means to delay the transmission to said input circuit of the biasing energy due to one of said momentary impulses with respgztto the operating energy due thereto until said one impulse has been transmitted through said device.

8. In combination, a space discharge repeater having input and out-put circuits, a receiving device in said output circuit, a plurality of resistances in said input circuit, a source 'of waves having impulse components representing speech and relatively steady components representing nolse, separate paths connectin said source to said resistances.. whereby t e drop in potential produced by noise components in one of said resistances nentralizes the drop in otential produced by noise components in t e other of said resistances, and means included be tween said source and said input circuit for causing the potential drop produced by speech components in one of -said resistances to be different from the drop in potential produced by speech components in the other of said resistances so that speech components only are transmitted through said repeater to said receiving device.

9. In combination, a space discharge device, an input and an output circuit there- `for, two resistances in series in said input circuit, a source of complex waves includlng impulsive and steady components, a receiving element in said output circuit'and responsive to said Waves, means comprising a path .connecting said source in shunt to one pf said resistances to cause the'production 1n said one resistance of a drop in potential corresponding to a portion 'of said complex wave at-a certain instant, a separate path connecting said source in shunt to the other of said resistances, and means in said sepa.- rate path comprising a delay circuit to cause the production in said other 'resistance at the same instant of a drop in potential corresponding to a portion of said complex wave at a' different instant, Athe resulting difference in potential :on said input circuit causing, waves from said source to be transmitted through said device to said receiving element.

10. In combination, a line over which speech impulses are transmitted, and subject to steady disturbing currents, as ace discharge device having an anode, a cat ode and a control electrode, a receiver element connected between said anode and cathode,

and responsive to energy variations transmitted through said devlce, two resistances and a battery connected in series betweenA said cathode and said control electrode, a path connecting said line in shunt to one of said resistances, a separate path connecting said line in shunt to the other of said resistances, said separate path comprising a space discharge device and a delay circuit. 11. In combination, a line over which momentar; impulses of current are transmitted, and su ject to steady disturbing currents, a space discharge device comprising an input and an output circuit and having a con-y trol electrode, a receiver element in said output circuit responsive to current variations transmitted through said space discharge device, two resistances in series in said input circuit, a path connectingsaid line in shunt to one of said resistances, whereby a dro in potential proportional to energy receive over said line is produced in said resistance,a separate path comprising a second space discharge device connecting said line in shunt tothe other of said resistances whereby a dro in potential proportional to ener y received over said line is produced in said other resistance o posing that produced in the first mentione resistance, said resistances being so proportioned with respect to each other that a resultant v negative potential varying in accordance with said disturbing current variatlons 1s Vmaintained on said control electrode by said variations therethrough but of insuciet magnitude to prevent operation of said device b said momentary impulses transmitted 12. In a voice-operated relay circuit, a-` path over which fluctuating voice' currents and relatively sustained alternating currents, may be transmitted, a space discharge device fed by said path and having a control elec.

trede, means to produce on said control electrode a continuous ne tive potential vary# ing inaccordance wit said sustained currents and at all times of suicient magnitude to prevent operation of said space discharge device by said sustained currents, and means to insure operation of said space discharge device by said voice currents.

witness whereof, I hereunto subscribe my name this 23 day of June A. D., 1925.

BJRN G. BJRNsoN. 

